Effects of Vitamin B₁₂-dependent Enzymes and Folate Compounds on Morphological Changes of Rhizobium meliloti

Abstract

The specific activities of three B₁₂-dependent enzymes in Rhizobium meliloti were compared in relation to morphological changes in the bacterium. The critical levels of ribonucleotide reductase and methylmalonyl-CoA mutase seemed to be maintained, while the level of methionine synthase was probably insufficient for cell multiplication. A close relationship was observed between the methionine synthase level and morphological changes in the bacterium. The addition of folate with methionine to the cobalt-deficient medium did not have a positive effect on bacterial growth. A sufficient amount of tetrahydrofolate was detected in the cobalt-deficient elongated cells. These findings might suggest the important role of methionine synthase in cell multiplication, which was unpredictable from the methylfolate trap hypothesis.